The following U.S. patents and non-U.S. patent publications are believed to represent the current state of the art:
U.S. Pat. Nos. 6,221,041; 6,715,520; 6,409,708; PCT US02/40596; WO 2004004806; WO 03086529; WO 9819724; WO 03/086530; WO 0035517 and WO 0211794.